1. Field of the Invention
The present invention relates to a decelerating system for decelerating the movement of sheets of paper or cardboard drawn into the delivery station of a sheet fed die cutting press.
2. Description of the Related Art
Die cutting presses are used for die cutting parts of paper or cardboard sheets which are fed through a die cutting press in rapid sequence so that the resulting die cut sheets can subsequently be formed into boxes and the like. Such sheet fed die cutting presses generally include an infeed station in which a pile of sheets is arranged with each sheet being successively taken from the top of the pile and carried onto a feed table. On this table each sheet is successively positioned against front lays and side guides prior to being seized on its leading edge by a series of grippers fitted along a crosswise gripper bar whose ends are attached to an endless train of lateral chains positioned on each side of the press and drawing the gripper bar and hence each sheet one-by-one through the press into the following processing stations. The processing stations generally include, in addition to the feed station and the feed table, the die cutting station, a waste stripping station, and a delivery station. The die cutting, of course takes place in the die cutting station and the die cut portions of each sheet have their waste removed in the waste stripping station and the finished die cut sheet is then delivered to the delivery station. At the delivery station, each sheet is released by the grippers on their respective gripper bars and the sheets are aligned and permitted to drop on top of a stack piling up on an outlet pallet.
In order to insure a uniform dropping and alignment of the sheets in the delivery station, the sheet should be as flat as possible once the sheet pulled into the delivery station is brought to a standstill when the grippers are opened. To this aim, when a sheet arrives in the delivery station, it is supported by a rear tablet at its trailing edge (and possibly by lateral tablets along its side) which may be retracted in order to let the sheet drop after it has come to a halt.
It will be understood that once a sheet has been die-cut and has had the waste portions of the sheet removed in the stripping station, the sheet may become quite frail and since it is drawn into the delivery station solely by the gripper bars gripping the leading edge of the sheet, the rapid deceleration of the gripper bar pulling the sheet into the delivery station may cause a curling or folding of the sheet.
In known die cutting presses, a decelerating device is utilized to create some friction on the die cut sheet as it moves into the delivery station and more particularly, such decelerating devices are known to consist of a long cross-wise brush extending transversely of the press with its bristles directed downwardly and in contact with the sheet after the leading edge of the sheet has passed beneath it whereby the remaining part of the sheet is pinched slightly between the brush and the rear tablet so as to retard or decelerate movement of the trailing edge of the sheet.
In such systems, however, the brush has to be raised regularly in order to avoid shocks caused to the brush from successive passage of the gripper bars between the brush and the rear tablet.
The brush is generally arranged on a slanted crossbar directed in a downstream direction with regard to the traveling direction of the sheet, whose ends are fitted so as to pivot around an axis arranged proximate to the upper edge of the brush. A biasing means, for instance one or several spiral springs fitted on the axle are located in a drum geared with a plate that is shaped as a sector of a circle and as part of an axle, and this biasing means keeps this crossbar and, hence the brush, at rest in an upper position. The brush is then set in to action by the application of a contrary rotation which is achieved by downward pressure exerted on an upper slanted lateral arm which is also part of the same axle.
The force with which the brush contacts the sheet and "pinches" it between the brush and the rear tablet is preferably set according to the fragility of the sheet as a consequence of the particular die cutting action being performed. This force can be modulated either by adjusting the rigidity of the bristles (such as by reinforcing the bristles with a pressure blade) or else by adjusting the final positioning of the brush relative to the traveling plane of the sheet and hence the rear tablet.
Moreover, the position of the rear tablet must be adjusted according to the size of the sheet to be used for a given press run so that the axle of the crossbar upon which the decelerating brush is mounted is fitted on either side of the station in a lateral groove or grooves of the delivery station in order to allow the manual repositioning of the rear tablet as well as the brush. The means for applying pressure on the upper arm of the lever then consists of a horizontal ramp or guideway which is actuated with a vertical orthogonal translational movement, this ramp extending over the whole setting area of the tablet and of the brush.
The decelerating action of the brush serving to pinch the sheet between the brush and the rear tablet is desirably reduced as the size of the sheets being delivered to the delivery station is reduced (as the distance from the leading to the trailing edges of the sheet is reduced) either by acting on the pressure applied by the brush against the sheet or by some other means until it becomes unnecessary to provide any particular decelerating forces to the sheets for very small sizes of sheet.
Manual settings of the brush and the rear tablet to accommodate sheets of different length from their leading to their trailing edges are time consuming and considerably increase machine down-time from one run to another run in which different sized sheets are die cut.